In the field of the above-described fabricated parts, the molding materials or molded articles are required to have well-balanced physical properties, such as moldability, dimensional accuracy, appearance, mechanical properties, e.g., tensile strength and bending strength, heat resistance, and the like. In particular, a good balance between appearance, such as surface gloss, and impact strength is demanded from the nature of exterior parts.
In general, impact strength includes Izod impact strength, Du Pont dart drop impact strength indicative of areal impact strength, etc. With the above-described particular purpose, the areal impact strength is considered more significant for practical use.
In an attempt of improving impact strength of rubber-modified styrene resins, a number of studies have hitherto been made. Known techniques include, for example, a method of blending a styrene-butadiene block copolymer and a method of blending an organopolysiloxane.
According to these known techniques, however, the amount of the modifier resin to be blended, such as the styrene-butadiene block copolymer, is relatively large, usually amounting to several percents or even more. As a result, it is very likely to deteriorate physical properties other than impact strength. In case of using the organopolysiloxane as a modifier, expected effects can be produced with a relatively small amount (less than 1%) to be blended so that serious deterioration in other physical properties is not observed. However, it is chiefly notched Izod impact strength that is improved by blending the organopolysiloxane, while the improving effect on areal impact strength, such as Du Pont dart drop impact strength, that seems practically more important, is still insufficient.